Most bacterial diseases begin with colonization of a particular mucosal surface (Beachey et al., 1981, J. Infect. Dis. 143:325-345). Successful colonization requires that an organism overcome mechanical cleansing of the mucosal surface and evade the local immune response. The process of colonization is dependent upon specialized microbial factors that promote binding to host cells (Hultgren et al., 1993 Cell, 73:887-901). In some cases the colonizing organism will subsequently enter (invade) these cells and survive intracellularly (Falkow, 1991, Cell 65:1099-1102).
Haemophilus influenzae is a common commensal organism of the human respiratory tract (Kuklinska and Kilian, 1984, Eur. J. Clin. Microbiol. 3:249-252). It is the most common cause of bacterial meningitis and a leading cause of other invasive (bacteraemic) diseases. In addition, this organism is responsible for a sizeable fraction of acute and chronic otitis media, sinusitis, bronchitis, and pneumonia.
Haemophilus influenzae is a human-specific organism that normally resides in the human nasopharynx and must colonize this site in order to avoid extinction. This microbe has a number of surface structures capable of promoting attachment to host cells (Guerina et al., 1982, J. Infect Dis. 146:564; Pichichero et al., 1982, Lancet ii:960-962; St Geme et al., 1993, Proc. Natl. Acad. Sci. U.S.A. 90:2875-2879). In addition, H. influenzae has acquired the capacity to enter and survive within these cells (Forsgren et al., 1994, Infect. Immun. 62:673-679; St Geme and Falkow, 1990, Infect. Immun. 58:4036-4044; St. Geme and Falkow, 1991, Infect. Immun. 59:1325-1333, Infect. Immun. 59:3366-3371). As a result, this bacterium is an important cause of both localized respiratory tract and systemic disease (Turk, 1984, J. Med. Microbiol. 18:1-16). Nonencapsulated, non-typable strains account for the majority of local disease (Turk, 1984, supra); in contrast, serotype b strains, which express a capsule composed of a polymer of ribose and ribitol-5-phosphate (PRP), are responsible for over 95% of cases of H. influenzae systemic disease (Turk, 1982, Clinical importance of Haemophilus influenzae, p. 3-9. In S. H. Sell and P. F. Wright (ed.), Haemophilus influenzae epidemiology, immunology, and prevention of disease. Elsevier/North-Holland Publishing Co., New York).
The initial step in the pathogenesis of disease due to H. influenzae involves colonization of the upper respiratory mucosa (Murphy et al., 1987, J. Infect. Dis. 5:723-731). Colonization with a particular strain may persist for weeks to months, and most individuals remain asymptomatic throughout this period (Spinola et al., 1986, I. Infect. Dis. 154:100-109). However, in certain circumstances colonization will be followed by contiguous spread within the respiratory tract, resulting in local disease in the middle ear, the sinuses, the conjunctiva, or the lungs. Alternatively, on occasion bacteria will penetrate the nasopharyngeal epithelial barrier and enter the bloodstream.
In vitro observations and animal studies suggest that bacterial surface appendages called pili (or fimbriae) play an important role in H. influenzae colonization. In 1982 two groups reported a correlation between piliation and increased attachment to human oropharyngeal epithelial cells and erythrocytes (Guerina et al., supra; Pichichero et al., supra). Other investigators have demonstrated that anti-pilus antibodies block in vitro attachment by piliated H. influenzae (Forney et al., 1992, J. Infect. Dis. 165:464-470; van Alphen et al., 1988, Infect. Immun. 56:1800-1806). Recently Weber et al. insertionally inactivated the pilus structural gene in an H. influenzae type b strain and thereby eliminated expression of pili; the resulting mutant exhibited a reduced capacity for colonization of year-old monkeys (Weber et al., 1991, Infect. Immun. 59:4724-4728).
A number of reports suggest that nonpilus factors also facilitate Haemophilus colonization. Using the human nasopharyngeal organ culture model, Farley et al. (1986, J. Infect. Dis. 161:274-280) and Loeb et al. (1988, Infect. Immun. 49:484-489) noted that nonpiliated type b strains were capable of mucosal attachment. Read and coworkers made similar observations upon examining nontypable strains in a model that employs nasal turbinate tissue in organ culture (1991, J. Infect Dis. 163:549-558). In the monkey colonization study by Weber et al. (1991, supra), nonpiliated organisms retained a capacity for colonization, though at reduced densities; moreover, among monkeys originally infected with the piliated strain, virtually all organisms recovered from the nasopharynx were nonpiliated. All of these observations are consistent with the finding that nasopharyngeal isolates from children colonized with H. influenzae are frequently nonpiliated (Mason et al., 1985, Infect. Immun. 49:98-103; Brinton et al., 1989, Pediatr. Infect. Dis. J. 8:554-561).
Previous studies have shown that H. influenzae are capable of entering (invading) cultured human epithelial cells via a pili-independent mechanism (St. Geme and Falkow, 1990, supra; St. Geme and Falkow, 1991, supra). Although H. influenzae is not generally considered an intracellular parasite, a recent report suggests that these in vitro findings may have an in vivo correlate (Forsgren et al., 1994, supra). Forsgren and coworkers examined adenoids from 10 children who had their adenoids removed because of longstanding secretory otitis media or adenoidal hypertrophy. In all 10 cases there were viable intracellular H. influenzae. Electron microscopy demonstrated that these organisms were concentrated in the reticular crypt epithelium and in macrophage-like cells in the subepithelial layer of tissue. One possibility is that bacterial entry into host cells provides a mechanism for evasion of the local immune response, thereby allowing persistence in the respiratory tract.
Thus, a vaccine for the therapeutic and prophylactic treatment of Haemophilus infection is desirable. Accordingly, it is an object of the present invention to provide for recombinant Haemophilus Adherence (HA) proteins and variants thereof, and to produce useful quantities of these HA proteins using recombinant DNA techniques.
It is a further object of the invention to provide recombinant nucleic acids encoding HA proteins, and expression vectors and host cells containing the nucleic acid encoding the HA protein.
An additional object of the invention is to provide monoclonal antibodies for the diagnosis of Haemophilus infection.
A further object of the invention is to provide methods for producing the HA proteins, and a vaccine comprising the HA proteins of the present invention. Methods for the therapeutic and prophylactic treatment of Haemophilus infection are also provided.